This invention relates to an apparatus for indicating a low fluid level in a pressurized canister, such as a pressurized starting fluid canister used in a starting fluid injection system for an internal combustion engine, or a disinfectant or deodorant canister used in an injection system for a forced air ventilation system.
One widely used type of fluid injection system includes a sealed, pressurized canister containing the fluid to be injected. This canister is connected to an injection nozzle by a conduit and an electromagnetic valve. On command, the valve is opened, thereby allowing pressurized fluid to escape from the canister for injection via the nozzle. Such systems are used, for example, to inject starting fluid into the intake manifold of an internal combustion engine as described in U.S. Pat. No. 4,202,309. Similarly, such systems have been proposed for use in introducing a disinfectant or deodorant into a forced air ventilation system, as described in my previous U.S. patent application Ser. No. 07/499,053.
One recurrent problem with such systems is that the user typically is not provided with any indication or warning that the canister is low on fluid. It would be advantageous if the user were provided with a warning indicating a low fluid condition in the canister. Of course, such a system should be reliable and low in cost if it is to achieve widespread acceptance.
In order to meet this need, my above identified U.S. patent application Ser. No. 07,499,053 described a low-fluid indicator useful in such systems. The disclosed low fluid indicator counts the total time the dispensing valve is commanded open and uses this count to calculate whether or not the treatment liquid supply in the sealed canister is near exhaustion. This calculation was based on the fact that the treatment liquid is discharged at a relatively constant flow rate through the injector nozzle, and this flow rate does not vary significantly as the level of liquid decreases in the canister. By multiplying the constant flow rate value by the total number of seconds the dispensing valve has been commanded open, the total amount of liquid dispensed from the canister is calculated. This amount is then compared with the known liquid capacity of the canister to determine if the fluid level in the canister is sufficiently low to require warning to the user. If the level of treatment liquid is determined to be excessively low, then an output indicator is activated to provide a suitable warning to the user.
The disclosed low fluid indicator functions well with systems in which the rate at which fluid is dispensed is substantially constant. The present invention is directed to an improved low fluid indicator that takes into account the variable flow rate through the valve under commonly encountered operating conditions. In this way, a more accurate and more reliable low fluid indicator can be provided.